Conventionally, the control modes of spindle motors in an optical storage drive include constant angular velocity (CAV) control mode and constant linear velocity (CLV) control mode. Generally, it is necessary to switch the spindle motor control modes between CAV control mode and CLV control mode when a seek operation is performed in the optical storage drive. It is very important that how to switch rapidly and accurately the control modes therebetween in order to improve the operation efficiency and stability of the optical storage drive simultaneously.
Taking an example of CAV control mode of the seek operation, FIG. 1 is one graph of the relationship between rotation speed and radial position of the optical disk in conventional CLV and CAV control modes. The dashed line represents the rotation speed profile from inner to outer radial position under CLV control mode. If the linear velocity of the optical disk is constant under CLV control mode, the rotation speed of the optical disk needs to be decreased progressively from inner to outer radial position.
As shown in FIG. 1, the solid curvy line from positions A to B represents the rotation speed profile from outer to inner circle of the optical disk under CAV control mode. When an optical pick-up (OPU) is moving from a starting position A to a target position B on the optical disk, it is required to calculate the rotation speed of target position B first. During the OPU movement, meanwhile, CAV control mode is employed to speed up or slow down the spindle motor of the optical storage drive. In FIG. 1, it is a speed-up case from position A and then transitionally tends to position B. Theoretically, when the OPU reaches the target position and the calculated rotation speed responsive to the target position is met, CLV control mode is then performed. However, in fact, the actual position switching to the target position is hard to decide exactly, and/or the difference between the actual rotation speed and the calculated rotation speed of the target position may be not close enough. Therefore, the timing switching to CLV control mode (i.e., from position C on solid line AC to position B on the dashed line) is too early and it is necessary to accelerate the rotation speed in position C via CLV control mode due to rotation speed difference between actual position C and target position B. Therefore, there is a great need of power consumption on acceleration of the rotation speed and more seeking time of the OPU is required.
Further, in one prior art of FIG. 1, switching to CLV control mode is performed according to whether the target position in the optical disk is sought or not. An estimated rotation speed at the target position will be calculated and the rotation speed is adjusted to achieve the estimated rotation speed by CAV control mode. However, as shown by solid line AC in FIG. 1, the estimated rotation speed may not meet the target rotation speed even though the OPU reaches the target position. In other words, after switching position A to position C, CAV control mode is instantly switched to CLV control mode but the CLV control status of the spindle motor is unstable because the rotation speed difference between position C and target position B is still large.
In another prior art of FIG. 2, the control modes of the spindle motor are switched therebetween on the basis of whether the rotation speed is high enough when a recording process is performed on the optical disk from inner to outer track or vice versa. However, when seeking operation is implemented, the position switch control or the rotation speed of the optical disk fails to meet criterion because the components assembly faults, limited position criterion or incorrect rotation speed threshold of the optical storage drive is employed. As shown in FIG. 2, estimated position D is far away from target position B, and offsets from the speed criterion, i.e. delta V, so that the control mode fails to be switched into the delta V. Furthermore, after switching position A to position D, the CLV control mode of the spindle motor is severely unstable because estimated position D considerably offsets from target position B.
Consequently, there is a need to develop a switching system and method to solve the above-mentioned problems.